(a) Field of the invention
The present invention relates to an improved phosphor complex and, more specifically, to an improved phosphor complex having high brightness which includes a conventional phosphor and a material which is adhered on the conventional phosphor, and capable of facilitating electron transfer.
(b) Description of the Related Arts
Generally, visible rays are emitted by almost all materials when the materials are heated at high temperatures. However, some materials luminate visible rays at ambient temperatures when an electron beam or ultraviolet light is radiated to the material. Generally, this phenomenon is called "luminescene" and the material causing this phenomenon is called a phosphor. Nowadays, phosphors, which are used in a Braun tubes, are prepared by mixing an activator with a host material and then calcinating them at 700.degree. C. to 1300.degree. C. for over 30 minutes. The host material includes oxide compounds of calcium, strontium, barium, beryllium, magnesium, zinc, cardium et al., sulfide compounds thereof, selenide compounds thereof, fluoride compounds thereof, silicate compounds thereof, phosphate compounds thereof, arsenate compounds thereof, and tungstate compounds (wolframate) thereof. In addition, manganese, magnesium, copper, bismuth, antimony, lead, titanium and various rare earth elements are used as the activators. In calcinating, a flux, which is a compound having good solubility for the phosphor, may also be used to grow the particle size of the phosphor.
Conventional zinc sulfide (ZnS) type phosphor comprises zinc and cadmium, which belongs to the IIb class of the Periodic table, and sulfur, selenide (Se), or tellurium (Te) which belong to the Vlb class of the Periodic table, as the host material. Copper, silver and gold, which belong to the lb class of the Periodic table are used as activators and aluminum and chloride are used as co-activators. Examples of ZnS type phosphor are ZnS: Cu, Au, Al (green phosphor) and ZnS:Ag, Cl (blue phosphor). ZnS type phosphor has been mainly used as phosphor for cathode ray tubes because the phosphor can luminate various visible rays by changing the host material or the activator. The ZnS type phosphors for cathode ray tubes are one of the most efficient types of phosphor. However, they have a disadvantage in that the Vd (dead voltage) at which luminescence starts is high and brightness saturation phenomena occur. Brightness saturation means that a further increase of brightness does not occur.
Furthermore, rare earth type phosphors are actively studied as red phosphor, and YVO.sub.4 :Eu is practically used as a red phosphor. The host material of thereof comprises a compound selected from, for example, YVO.sub.4, Y.sub.2 O.sub.2 S, La.sub.2 O.sub.2 S and Gd.sub.2 O.sub.2 S et al. Moreover, rare earth elements comprising europium (Eu), terbium (Tb), samarium (Sm), cerium (Ce), and/or praseodymium (Pr) are mainly used as the activators. The characteristic of the phosphor is that its energy efficiency is lower than ZnS type group phosphors, but brightness saturation does not occur. The phosphors which luminate red color, among the above phosphors, are Y.sub.2 O.sub.3 :Eu.sup.3+ and Y(V, P)O.sub.4 :Eu.sup.3+. Recently, Y.sub.2 O.sub.2 S:Eu.sup.3+ has been developed as a rare earth type red phosphor.
In the mean time, phosphors can be classified into white, red, green, yellow and blue phosphors by their colors. Nowadays, three colors, red, green and blue (R. G. B) phosphors are mainly used. Until recently, green phosphor has been actively developed, and examples thereof are (ZnCd)S:Cu,Al, ZnS:Cu,Al, ZnS:Cu,Al,Au, Zn.sub.2 SiO.sub.4 :Mn, Zn.sub.2 SiO.sub.4 :Mn,As, ZnO, and (ZnCd):S:Cu,Al, et al.
Nowadays, demand for color display devices ("CDTs") have increased according to the development of multimedia, and thereby a phosphor having higher brightness than the present phosphors is required. The improvement of brightness of phosphor is an essential to improve quality and increase precision of Braun tubes.
Recently, a sensitizer has been added to the phosphor in order to increase the brightness of red phosphor. In order to increase the brightness of green phosphor, a compound selected from Bi, Tb and Sb, et al., is added to the phosphor. Furthermore, in order to increase the brightness of blue phosphor, a material which is capable of facilitating electron-hole pairs transfer or a sensitizer is added to the phosphor. A co-activator having a wavelength of luminating spectrum corresponding to the wavelength of absorption spectrum of an activator is used as the sensitizer.
However, the above methods have disadvantages in that they are complicated and difficult because a conventional process for preparing a phosphor and condition thereof should be changed by additionally using sensitizers or Bi, Tb and Se, et al. Furthermore, the brightness of the phosphors was not increased as expected by the above methods.